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Error code reference

LG Air Conditioner Error Code 138

Sub2 outdoor unit excessive cooling inlet temperature sensor open or short (3 units).

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What the 138 error code actually means

Your LG air conditioner's outdoor unit has detected a problem with a temperature sensor that monitors the cooling intake on one of the connected outdoor units. The sensor is either not sending a signal at all or sending a signal that doesn't make sense, so the system has stopped normal operation to protect itself. A technician will need to inspect the sensor wiring and test the sensor to determine whether the sensor or its wiring needs to be replaced.

Diagnostic procedure

The full 138 procedure

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First diagnostic step
Check connection status of the sensor; measure sensor resistance.
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Most common causes of 138

Ranked by how often they cause this code
  1. 1Loose or disconnected sensor connector
  2. 2Failed NTC thermistor sensor
  3. 3Damaged wiring harness
  4. 4Corroded connector terminals
  5. 5Faulty outdoor unit control board

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Questions people ask about 138

What does 138 mean on a LG air_conditioner?
Error code 138 indicates that the excessive cooling inlet temperature sensor on the Sub2 outdoor unit in a three-unit system has been detected as open or shorted. This means the control system is receiving a signal that is outside the valid range, either because the sensor has failed, the wiring is damaged, or a connector has come loose. The system flags this fault to prevent operation under unmonitored temperature conditions.
Is it safe to run my LG air conditioner with error code 138 active?
Running the system with this fault active is not recommended. The inlet temperature sensor provides the controller with data needed to regulate cooling operation on the Sub2 outdoor unit. Operating without valid sensor input can lead to improper refrigerant management or undetected temperature extremes that may cause further component damage.
How much does it cost to repair LG error code 138?
Repair costs vary depending on what is actually faulty. A replacement NTC thermistor sensor typically falls in the range of $15 to $60 for the part alone. If the wiring harness needs repair or replacement, labor and materials could bring the total to $100 to $250 or more. A failed outdoor unit control board is the most expensive scenario, with parts and labor potentially ranging from $300 to $600 or higher depending on the model.
Can I fix LG error code 138 myself?
A knowledgeable DIYer can start by checking that all sensor connectors on the Sub2 outdoor unit are firmly seated and free of corrosion. If connections look good, measuring the thermistor resistance with a multimeter is the next step. However, accessing outdoor unit control boards and refrigerant-side components typically requires professional tools and training, so complex wiring or board issues are best handled by a certified technician.
Will resetting my LG air conditioner clear error code 138?
A power reset may temporarily clear the error from the display, but if the underlying sensor fault is still present, the code will return once the system restarts and re-checks the sensor circuit. The fault must be resolved at the hardware level by repairing or replacing the sensor or wiring before the code will stay cleared.

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